Arterial thrombosis of both native artery and bypass grafts in addition to pulmonary embolic disease have significant associated morbidity and mortality due to the disease process as well as the surgical and the non- surgical therapeutic treatments. Currently non surgical treatments employ thrombolytic intra-arterial or systemic agents such as Urokinase. These lytic agents are relatively safe but may have complications such as stroke, bleeding and dot embolization. Therapy may be protracted resulting in further ischemia and possible tissue loss. These procedures are often 48-72 hours long and require expensive intensive care monitoring. It is desirable to accelerate clot lysis thereby reducing the risks and costs associated with the procedure and minimizing morbidity. In this study we propose the use of intravascular ultrasound in conjunction with thrombolytic agent to increase the rate of thrombolysis. In-vivo experiments will be conducted to determine the best possible sonication conditions. Based on these results a catheter system that enables simultaneous delivery of ultrasound and thrombolytic agent will be designed and implemented. Using this system animal studies will be carried out to determine the effectiveness of the proposed technique. We believe that the use of ultrasound in combination with the thrombolytic agent may reduce the cost of treatment and also the morbidity associated with multitude vascular diseases involving arterial and aft thrombosis.